WO1999043954A1

WO1999043954A1 - Ring gate control system for francis turbine

Info

Publication number: WO1999043954A1
Application number: PCT/EP1999/001214
Authority: WO
Inventors: Karl Oettle; Jose Claudio Mazzoleni
Original assignee: Voith Hydro Gmbh & Co. Kg; Voith Hydro, Inc.
Priority date: 1998-02-27
Filing date: 1999-02-25
Publication date: 1999-09-02
Also published as: CN1292065A; CN1084439C

Abstract

A control system for a ring gate (134) disposed in a hydraulic turbine installation in which water flows through a water passageway from an upstream reservoir past a turbine runner (126). The ring gate surrounds the runner and is mounted for longitudinal movement between an open position in which the water flow is unencumbered and a closed position in which the water flow is shut off. The control system includes a set of actuators (146), a set of operating rods, and an electrical control circuit. The actuators are installed above the ring gate and distributed around its circumference. Each operating rod is connected to the ring gate and an associated actuator. The electrical control circuit controls and synchronizes the actuators and thereby controls the movement of the ring gate. A turbine installation including the ring gate control system is provided along with a method for controlling the movement of the ring gate. A method of utilizing the actuators as a jacking system to lift the head cover and thereby ease maintenance is also disclosed.

Description

RING GATE CONTROL SYSTEM FOR FRANCIS TURBINE

Field of the Invention The present invention relates generally to hydroelectric turbine installations. More particularly, this invention pertains to hydroelectric installations utilizing ring gates to shut-off the water flow from an upstream reservoir. Even more particularly, this invention relates to a control system for synchronizing the actuators of such ring gates .

Background of the Invention

Ring gates (or cylindrical gates) in hydroelectric and pump turbines may be used in place of the conventional butterfly or spherical valves normally used as penstock shut-off devices, to close off water flow from the upstream reservoir. The ring gate serves as an isolating valve located in the distributor of the turbine, typically between the stay vanes and the wicket gates. An advantage of the ring gate over a conventional penstock shut-off device is that no powerhouse extension is required, thus significantly reducing costs. Another advantage of the ring gate is the elimination of efficiency losses associated with the conventional penstock valves. That is, unlike the butterfly type valve in which some components (e.g., the butterfly plate centrally located within the water supply tube) remain in the water flow^' even when the valve is fully open, all - 2 - components of the ring gate are completely retracted from the water flow path when the gate is fully open. Moreover, unlrke the spherical type valve, no reduction in tube diameter is associated with the water flow shut- off device.

The ring gate is a thin, short cylinder surrounding the turbine runner which, in the closed position, blocks the water flow passage between the distributor and the stay ring. In the open position, the ring gate cylinder is housed in a compartment formed between the stay ring and head cover, where it remains completely retracted from the water flow passage. In normal operation, the ring gate closes once the wicket gates are closed and, at unit start-up, the ring gate opens before the wicket gates start to open. For emergency conditions, the ring gate may be called upon to close against full flow.

A partially schematic representation of a prior art ring gate cylinder 10 is shown in Figure 3. Ring gate 10 is operated by a set of actuators 12 positioned at spaced location around an upper circumference 14 of the ring gate, that is, at positions they would occupy as if mounted to the head cover (as typical) . The actuators 12 may be either of the rotary type high torque, low speed, oil motors or of the linear type servomotors. The details of a typical prior art rotary type actuator 12 are shown in Figure 2. Rotary actuator 12 includes an oil motor 16, a spring 18, a screw 20, a support 22, and a lifting stem 24 coupled to ring gate 10.

The heretofore known method of synchronizing either of the above-described prior art actuators was by mechanically coupling pairs of adjacent actuators together with chain loops. That is, each two adjacent actuators 12 were connected by a continuous chain loop 16 so that, for example, a total of six chain loops were required for a six actuator arrangement (as illustrated) . With this system, it was also necessary to provide each - 3 - chain loop 26 with its own chain tensioner 28, so that proper tension could be individually maintained. An example of a ring gate employing chain loops for mechanical synchronization of the actuators is disclosed in U.S. Patent No. 4,434,964 to Hudon.

The known hydraulic circuits for controlling the ring gate actuators comprise a pressure system and control valves which govern the flow of hydraulic fluid to and from the actuators for closing and opening the ring gate. For a rotary type actuator, it is known to obtain the linear motion for the ring gate by a screw rotating in a nut secured to the lifting stem of the ring gate, and the rotary motion for the synchronizing chains is obtained by direct coupling to the oil motors. For a linear type actuator, it is known to obtain the linear motion for the ring gate by direct coupling to the piston. More specifically, the rotary motion for the synchronizing chains is obtained via a roller screw system in which a roller nut is secured to the servomotor piston. The above mentioned patent to Hudon discloses a similar coupling.

The known mechanical control systems for ring gates in hydroelectric turbines have many mechanical parts subject to wear and tear (e.g., the chain loops and sprockets) , and which also require laborious adjustment (e.g., the chain loop tensioner). Modern hydroelectric turbines are typically equipped with electrical control systems in which operational modes and parameters can be adapted to new functional needs, such as the control of the ring gate travel speed. In addition, electrical control systems permit introduction of new functional features such as capability of easing maintenance to the water passages by lifting the head cover with the ring gate actuators acting as a jacking system. Moreover, with the advent of high speed digital processing and precision position sensors, used in conjunction with modern hydraulic technology, the present ring gate - 4 - control system is able to function with substantial accuracy. At the same time, the laborious installation and set up time found in older systems are eliminated. As an added benefit, such a system makes the turbine pit less crowded, hence easier for maintenance.

Summary of the Invention The present invention includes a control system for a ring gate disposed in a hydraulic turbine installation in which water from an upstream reservoir flows past a turbine runner. The ring gate surrounds the turbine runner and is mounted for longitudinal movement along the turbine axis between an open position in which the water flow is unencumbered and a closed position in which the water flow is shut off. The control system further comprises a set of actuators, a set of operating rods, and an electrical control circuit. The actuators are installed in longitudinal alignment with a circumference of the ring gate and are also distributed therearound. Each operating rod has one end connected to the ring gate and another end connected to an associated actuator. The electrical control circuit controls and synchronizes the set of actuators and thereby controls the movement of the ring gate . According to a preferred aspect of the invention, the actuators are hydraulic cylinders and the control system further includes a set of metering devices coupled to a common shaft for providing a substantially equal flow of hydraulic fluid to each cylinder. According to a particularly preferred aspect of the invention, each cylinder is coupled to a discharge valve responsive to electrical signals from an electrical controller for draining fluid from the associated cylinder to thereby speed up or slow down movement of the cylinder.

The present invention also includes a hydraulic turbine installation comprising a water flow passage for containing turbine components and a turbine runner disposed for rotation about a longitudinal axis in the passage so that water flowing therethrough impinges on the runner. The turbine runner is surrounded by a ring gate disposed for longitudinal movement between an open position in which the water flow impinging on the runner is unencumbered by the ring gate and a closed position in which the water flow is prevented from impinging on the runner. A set of actuators is installed in longitudinal alignment with and distributed around a circumference of the ring gate, and each actuator is connected to the ring gate by an operating rod. An electrical control circuit is provided for controlling and synchronizing the set of actuators, to thereby control the movement of the ring gate.

The present invention also features a method for controlling movement of a ring gate in a hydraulic turbine installation. The method comprises the steps of setting a desired direction and approximate speed for the set of actuators, monitoring the set of actuators to detect when at least one actuator is lagging or leading other actuators, and adjusting the speed of the at least one lagging or leading actuator to synchronize the set of actuators . A method of lifting a head cover in the turbine installation to ease maintenance is also provided. The method comprises the steps of raising the ring gate to obtain a desired clearance distance between the ring gate and the discharge ring. A plurality of jacking supports are then positioned in the clearance distance beneath the ring gate. Next, the ring gate is lowered until the ring gate presses against the jacking stand. As the actuators continue to attempt to lower the ring gate, the actuators and head cover are lifted a desired distance above the runner.

Other advantages and features of the invention will become apparent from the detailed description given - 6 - hereinafter. It should be understood, however, that the detailed description and specific embodiments are given by way of illustration only since, from this detailed description, various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.

Brief Description of the Drawings The preferred exemplary embodiment of the invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements and:

Figure 1 is an elevational view, partially in cross section, of a Francis turbine installation including a ring gate surrounding the turbine runner, the ring gate being shown in a partially closed position;

Figure 2 is an enlarged elevational view, partially in cross section, of a prior art hydraulic rotary type servomotor mounted for actuating a ring gate; Figure 3 is a partially schematic, perspective view of a ring gate and a prior art chain loop arrangement for synchronizing movement of six prior art hydraulic servomotors as shown in Figure 2 ;

Figure 4 is an enlarged elevational view, partially in cross section, of an hydraulic servomotor with an internal feedback device in accordance with the present invention;

Figure 5 is a partially schematic, perspective view of a ring gate and a plurality of hydraulic servomotors as shown in Figure 4, the servomotors being shown distributed around the circumference of the ring gate;

Figure 6 is a schematic representation of a ring gate control system including a hydraulic control circuit and an electrical control circuit for synchronizing the servomotors and controlling the ring gate shown in Figure 5; and Figure 7 is an elevational view, partially in cross section, of a Francis turbine installation including a ring gate and ring gate actuators being used as a jacking system for lifting the head cover.

Detailed Description of a Preferred Exemplary Embodiment The present invention relates generally to a control system for a ring gate (or cylindrical gate), in a hydroelectric turbine installation. More particularly, the invention relates to a system for electronically monitoring and controlling the actuators of the ring gate to selectively close off the water flow through the turbine water passage. Referring to Figure 1, a portion of a hydroelectric turbine installation 100 comprises a passageway 102, in which water flows from an upstream reservoir 104 to a downstream discharge region 106. Turbine installation 100 is illustrated as a Francis turbine including a runner 108, a head cover 110, upper and lower stay ring shrouds 112, 113, a bottom/discharge ring 114 and a draft tube 116. Stay rings 112, 113, head cover 110, bottom/discharge ring 114 and draft tube 116 are stationary components which together form a housing through which the water flows. Runner 108 is secured

(e.g., by bolts 118) to a shaft 120 for rotation about a longitudinal axis 122 so that runner 108 rotates as the water flow through passageway 102 impinges on runner 108. Runner 108 includes a crown 124 and a plurality of circumferentially spaced runner blades 126 extending from crown 124 to an enclosing band 128 substantially concentric therewith. A plurality of stay vanes 130 extend between the upper and lower stay ring shrouds 112, 113, and a plurality of pivotal wicket gates 132 are adjustable to regulate the water flow impinging on runner 108. Installation 100 further includes a ring gate cylinder 134 surrounding runner 108, and substantially concentric therewith, for selectively shutting off the water flow through passageway 102. Ring gate 134 is mounted for guided longitudinal movement along axis 122 between an open position and a closed position. In the open position, ring gate 134 is fully raised into a compartment 136 formed between stay ring 112 and head cover 110, where it is completely removed from the water flow in passageway 102. In the closed position, ring gate 134 is fully lowered against a stop 138, where it completely blocks the water flow through passageway 102 and thus prevents the water flow from impinging on runner 108. In Figure 1, ring gate 134 is illustrated partway between the open and close positions for clarity of illustration, but ring gate 134 will normally be in the fully raised or lowered position except when moving between the two positions.

A number of ring gate guides 140, 142 and 144 are preferably positioned on head cover 110, stay ring 112 and stay vanes 130, respectively, to limit radial movement and deformation of ring gate 134. Guides 140, 142 and 144 may be made of stainless steel or bronze or some other suitable material which provides the above described objectives.

Turning now to Figure 5, a set of actuators 146 is illustrated in longitudinal alignment with an upper circumference 148 of ring gate 134. Although the illustrated control system includes five actuators, more or fewer actuators could of course be used; however, at least three actuators are typically required. Regardless the exact number, actuators 146 are distributed at generally equidistant locations from each other around circumference 148, and each actuator 146 is mechanically coupled to ring gate 134 by an operating rod (or lifting stem) 150. Actuators 146 are also electrically coupled to an electrical control circuit (as described below with " "™* * PCT/EP99/01214

- 9 - reference to Figure 6) which controls and synchronizes the movement of actuators 146, to thereby control the movement of ring gate 134.

Turning now to Figure 4, an enlarged sectional view of one suitable actuator 146 is shown in the fully retracted (or raised) position. Actuator 146 is a linear type hydraulic cylinder including a hollow casing 152 defining a chamber 154, and a movable piston 156 dividing chamber 154 into an upper side 158 and a lower side 160. Operating rod 150 is secured to piston 156 at an upper end 162 and extends downwardly to a lower end 164 secured (e.g., by a threaded rod 166) to upper circumference 148 of ring gate 134. Actuator 146 also includes a fluid in/out upper line 168 and a fluid in/out lower line 170. Upper and lower lines 168, 170 fluidly couple the respective upper and lower sides 158, 160 of chamber 154 to a source or sump of hydraulic fluid (as described below with reference to Figure 6) . Actuator 146 further includes a sensor 172 which selectively generates electrical signals indicative of the instantaneous position of piston 156 in chamber 154. Each sensor 172 is preferably a digital position transducer which may, for convenience, be integrated internally of actuator casing 152. Turning now to Figure 6, a ring gate control system generally designated as 174 will be described. As will become clear below, control system 174 is a two- stage control system in which a direction and approximate speed for the set of actuators 146 is set as a group, while comparatively fine adjustments are made in the speed of individual actuators 146. Control system 174 includes a hydraulic control circuit generally designated as 176 and an electrical control circuit generally designated as 178; which cooperate with each other to control movement of ring gate 134. Hydraulic control circuit 176 includes a number of components (as detailed below) interconnected by the fluid couplings shown in - 10 - solid lines. Similarly, electrical control circuit 178 includes a number of components (as detailed below) interconnected by the electrical couplings shown in phantom lines. Hydraulic control circuit 176 includes, in addition to the set of hydraulic cylinders 146, the components of an oil pressure system 180, a sump 182, a proportional valve 184, a set of hydraulic motors 186, and a set of discharge valves 188. The combination of proportional valve 184 and the set of hydraulic motors

186 permits electrical control circuit 178 to control the direction and approximate speed of actuators 146. At the same time, the set of discharge valves 188 permits electrical control circuit 178 to make relatively fine adjustments in the speed of individual actuators 146.

Preferably, proportional valve 184 is an electrically operated speed control proportional valve assembly which includes an "up" position 190 and a "down" position 192. Motors 186 are fluidly coupled to a common fluid in/out line 194 of proportional valve 184, and each motor 186 is also fluidly coupled to the lower in/out fluid line 170 of one associated cylinder 146. That is, each motor 186 is interposed along the fluid coupling between the associated cylinder 146 and proportional valve 184. Each motor 186 is also mechanically coupled to a common shaft 195 so that all motors 186 rotate at the same speed. In addition, each motor 186 is preferably spaced at about the same distance from the associated hydraulic cylinder 146 to equalize pressure drops. Thus, motors 186 act as flow dividers which meter approximately equal flows of oil to/from cylinders 146.

As one skilled in the art will know, each motor 186 in the set of hydraulic motors 186 will not be exactly equal, that is, even when rotating at identical speeds one of them can allow a slightly different flow of oil to pass than the others. Accurate synchronization of cylinders 146 is of primary importance in maintaining the - 11 - levelness of ring gate 134 to prevent bending thereof and possible gouging of the guide slot. Accordingly, the speed of each cylinder 146 is preferably fine tuned individually by one associated discharge valve 188. More specifically, each discharge valve 188 is interposed along the fluid coupling between one associated hydraulic motor (or metering device) 186 and the associated cylinder 146. Each discharge valve 188 is an electrically operated valve capable of selectively draining fluid from the associated cylinder 146 to an associated sump 196. That is, each discharge valve 188 has an open position 198 (which allows the fluid to drain from the associated lower side chamber 160) and a closed position 200. Alternatively, each discharge valve 188 could be configured drain the fluid back to oil pressure system 180 through some sort of sort of recirculation circuit, to thereby improve efficiency of hydraulic circuit 176. Preferably, a set of variable restriction flow valves 202 are also provided to fine tune the rate of discharge through each valve 188. If so, each variable restriction flow valve 202 is interposed between one associated discharge valve 188 and the associated sump 196.

Electrical control circuit 178 includes, in addition to the set of sensors 172, the components of a digital-based programmable logic controller (or PLC) 204, a pair of solenoids 206, 208 associated with proportional valve 184, and a set of solenoids 210 associated with the set of discharge valves 188. PLC 204 is electrically coupled by electrical lines 212, 214 to signal inputs of the respective solenoids 206, 208 for controlling the position of proportional valve 184 (i.e., for moving valve 184 from the "neutral" position to the "up" or "down" position, and vice versa) . PLC 204 is also electrically coupled by electrical lines 216 to signal outputs of sensors 172 for sensing the positions of pistons 156 within cylinders 146. In addition, PLC 204 - 12 - is electrically coupled by electrical lines 218 to signal inputs of solenoids 210 for controlling the positions of discharge valves 188 (i.e., for moving valves 188 from the closed position to the open position) . More specifically, when one solenoid 210 is energized, the associated discharge valve 188 moves to the open position 198 and, when the solenoid is not energized (or de- energized) , an associated return spring 220 returns (or biases) valve 188 to the closed position 200. Now that turbine installation 100 and the associated ring gate control system 174 have been described, a method of controlling the movement of ring gate 134 will doe provided. To raise ring gate 134 to the open (or turbine operational) position, an electrical control signal is generated by PLC 204 and sent to solenoid 208 to move proportional valve 184 to the "up" position 190. This allows pressurized oil to flow from oil pressure system 180 to the set of hydraulic motors 186, thereby causing motors 186 to rotate at identical speeds on common shaft 195 and meter approximately equal amounts of oil to lower sides 160 of associated cylinders 146.

As mentioned above, however, motors 186 may not be exactly equal. If one of them, for instance, allows a slightly higher oil flow to pass than the others, the associated cylinder 146 will move slightly faster than the others (i.e., the piston 156 thereof will reach a slightly higher position than the other pistons 156) . To detect this condition, PLC 204 monitors the electrical outputs of sensors 172. When PLC 204 detects one cylinder 146 at a slightly higher position than the other cylinders 146, PLC 204 generates an electrical control signal and sends it to the electrical input of the associated solenoid 210 of the leading cylinder 146. This allows a small amount of oil to drain from the lower side 160 of the leading cylinder 146 to the associated - 13 - sump 196, which brings it down (or retards it) to the same level as the remaining cylinders 146.

Similarly, to lower ring gate 134 to the closed position (i.e., to shut off the water flow through passageway 102) , an electrical control signal is generated by PLC 204 and sent to solenoid 206 to move proportional valve 184 to the "down" position 192. This applies pressure to upper sides 158 of cylinders 146, and the oil on lower sides 160 of cylinders 146 flows through hydraulic motors 186, again turning at the same speed on common shaft 195. The oil flowing through hydraulic motors 186 passes through proportional valve 184 to sump 182 (or alternatively, back to oil pressure system 180 through a recirculation circuit) . During this process, if one cylinder 146 starts traveling slower than the others (i.e., again by one piston 156 staying higher than the others) , PLC 204 detects this condition by monitoring sensors 172. To correct the position, PLC 204 generates an electrical control signal and sends it to the associated solenoid valve 188 of the lagging cylinder 146 to drain a small amount of oil from lower side 160 to the associated sump 196. Thus, the lagging cylinder 146 is brought down (or accelerated) to the same level as the remaining cylinders 146.

Referring now to Figure 7, a method of lifting head cover 110 to facilitate the maintenance of water passageway 102, turbine runner 108, and associated components will now be described. Ring gate cylinder 134 is raised to its open position, and the water flow through passageway 102 is shut off by some external means (not shown) . A plurality of jacking stands (or supports) 222 are then positioned beneath ring gate 134 in longitudinal alignment with a lower circumference 224 of the open ring gate 134. About ten jacking stands of a height X are preferably used, but the actual number is not critical so long as it is at least three. Regardless - 14 - of the exact number, jacking stands 222 are distributed at generally equidistant locations from each other around lower circumference 224. Head cover bolts 226 are removed from a head cover support barrel 228; thus, actuators 146 are free of stay ring 112 but bolted to head cover 110.

Ring gate 134 is then lowered until lower circumference 224 of ring gate 134 abuts the tops of jacking stands 222. Jacking stands 222 are sufficiently strong and rigid enough to bear the weight of head cover 110, actuators 146, operating rods 150, ring gate 134, and any other associated components. Thus, any further lowering of ring gate 134 by actuators 146 causes actuators 146, head cover 110, and the associated components to be lifted above their normal operating positions. When operating rods 150 are fully extended by the distance X, head cover 110 is positioned at the distance X above runner 108. The reverse procedure can of course be used to lower head cover 110. Accordingly, this method permits actuators 146 to function as a jacking system for creating substantial room in the turbine pit, thus easing maintenance. Notably, this method of raising head cover 110 is not possible with the conventional mechanical synchronizing systems described in the above background section. The mechanical synchronizing systems require chain links that typically are anchored to the pit liner. This prevents the actuators from being raised, and hence the head cover cannot be lifted. Although a variety of embodiments have been particularly described, it should be understood that the above description is of preferred exemplary embodiments of the present invention, and that the invention is not limited to the specific forms described. For example, the vertically oriented ring gate illustrated could be horizontal if associated with a horizontally oriented turbine. In addition, the ring gate could be housed in a - 15 - chamber below the lower shroud of the stay ring and then moved upward to the closed position to shut-off the water flow. Moreover, the present invention could be integrated with a Kaplan type turbine or some other type of turbine, or even a pump. Such other constructions are, nevertheless, considered to be within the scope of this invention. Accordingly, these and other substitutions, modifications, changes and omissions may be made in the design and arrangement of the elements as disclosed herein without departing from the scope of the appended claims.

Claims

- 16 - Claims What is claimed is:

1. A control system for a ring gate in a hydraulic turbine installation including a turbine runner rotating on a longitudinal axis, the ring gate being concentric with the turbine runner and disposed for longitudinal movement between an open position in which water flow from an upstream reservoir is substantially unencumbered and a closed position in which the water flow is substantially shut off, the control system comprising: a set of actuators installed in longitudinal alignment with a circumference of the ring gate and distributed around the circumference; a set of operating rods, each rod having one end connected to the ring gate and the other end connected to an associated actuator; and an electrical control circuit for controlling and synchronizing the set of actuators and thereby controlling the movement of the ring gate.

2. The control system of claim 1, wherein the actuators are hydraulic cylinders, the control system further comprising: a set of metering devices, each metering device fluidly coupled to an associated cylinder and spaced a predetermined distance therefrom; and an electrically operated valve assembly including at least one electrical input and disposed to fluidly couple the set of metering devices to a fluid source or sump, the valve controlling a flow of hydraulic fluid between the source or sump and the metering devices in response to electric control signals applied to the at least one electrical input from the electrical control circuit . - 17 -

3. The control system of claim 2, wherein the electrically operated valve assembly is a speed control proportional valve with separate up and down electrical inputs .

4. The control system of claim 2, wherein the metering devices are hydraulic motors, and wherein the predetermined distances between the metering devices and the associated cylinders are all substantially equal.

5. The control system of claim 2, wherein the metering devices are hydraulic motors coupled to a common shaft, whereby the motors rotate at equal speeds and meter approximately equal amounts of hydraulic fluid.

6. The control system of claim 2, further including a set of electrical valves, each electrical valve including at least one electrical input and disposed to fluidly couple an associated cylinder to the source or sump, each electrical valve discharging hydraulic fluid from the associated cylinder into the source or sump in response to electric control signals applied to the at least one electrical input from the electrical control circuit.

7. The control system of claim 6, wherein the set of electrical valves is a set of solenoid valves.

8. The control system of claim 6, wherein each hydraulic cylinder has a movable piston located in a chamber thereof which divides the chamber into a lower side and an upper side, and wherein each metering device of the set of metering devices and each electrical valve of the set of electrical valves is fluidly coupled to the lower side of the chamber of the associated cylinder. - 18 -

9. The control system of claim 8, further comprising a plurality of sensors selectively generating electrical signals indicative of the positions of the pistons in the chambers of the set of hydraulic cylinders.

10. The control system of claim 1, further comprising : a plurality of sensors selectively generating electrical signals indicative of positions of the actuators ; an electrical controller for receiving and processing the electrical signals from the sensors and for generating control signals; and means for adjusting the speed of individual actuators responsive to the control signals to synchronize the actuators and control the movement of the ring gate.

11. The control system of claim 10, wherein the controller is a digital-based programmable logic controller capable of generating digital control signals.

12. The control system of claim 10, wherein each sensor of the plurality of sensors is a digital position transducer.

13. The control system of claim 1, further comprising : primary control means for substantially controlling speed and direction of the actuators; and secondary control means for making relatively small adjustments in the speed of the actuators.

14. The control system of claim 1, wherein the turbine axis is vertical and the actuators are mounted above the circumference of the ring gate. - 19 -

15. A hydraulic turbine installation, comprising: a water passage for containing turbine components and extending from an upstream reservoir of water to a downstream discharge region; a turbine runner disposed for rotation about a longitudinal axis in the passage so that water flowing therethrough impinges on the runner; a ring gate concentric with and spaced outwardly from the turbine runner, the ring gate disposed for longitudinal movement between an open position in which the water flow impinging on the runner is unencumbered by the ring gate and a 'dosed position in which the water flow is substantially prevented from impinging on the runner; a set of actuators installed in longitudinal alignment with a circumference of the ring gate and distributed around the circumference; a set of operating rods, each rod having one end connected to the ring gate and the other end connected to an associated actuator; and an electrical control circuit for controlling and synchronizing control of the set of actuators and thereby controlling the movement of the ring gate.

16. The turbine installation of claim 15, wherein the actuators are hydraulic cylinders, the installation further comprising: a set of metering devices, each metering device fluidly coupled to an associated cylinder and spaced a predetermined distance therefrom; and an electrically operated valve assembly including at least one electrical input and disposed to fluidly couple the set of metering devices to a fluid source or sump, the valve controlling a flow of hydraulic fluid between the source or sump and the metering devices in response to electric control signals applied to the at - 20 - least one electrical input from the electrical control circuit .

17. The turbine installation of claim 16, wherein the electrically operated valve assembly is a speed control proportional valve with separate up and down electrical inputs.

18. The turbine installation of claim 16, wherein the metering devices are hydraulic motors, and wherein the predetermined distances between the metering devices and the associated cylinders are all substantially equal.

19. The turbine installation of claim 16, wherein the metering devices are hydraulic motors coupled to a common shaft , whereby the motors rotate at equal speeds and meter approximately equal amounts of hydraulic fluid.

20. The turbine installation of claim 16, further including a set of electrical valves, each electrical valve including at least one electrical input and disposed to fluidly couple an associated cylinder to the source or sump, each electrical valve discharging hydraulic fluid from the associated cylinder into the source or sump in response to electric control signals applied to the at least one electrical input from the electrical control circuit.

21. The turbine installation of claim 20, wherein each hydraulic cylinder has a movable piston located in a chamber thereof which divides the chamber into a lower side and an upper side, and wherein each metering device of the set of metering devices and each electrical valve of the set of electrical valves is fluidly coupled to the lower side of the chamber of the associated cylinder. - 21 -

22. The turbine installation of claim 21, further comprising a plurality of sensors selectively generating electrical signals indicative of the positions of the pistons in the chambers of the set of hydraulic cylinders.

23. The turbine installation of claim 15, further comprising : a plurality of sensors selectively generating electrical signals indicative of positions of the actuators; an electrical controller for receiving and processing the electrical signals from the sensors and for generating control signals; and means for adjusting the speed of individual actuators responsive to the control signals to synchronize the actuators and thereby control the movement of the ring gate.

24. The turbine installation of claim 15, further comprising : primary control means for substantially controlling speed and direction of the actuators; and secondary control means for making relatively small adjustments in the speed of the actuators.

25. The turbine installation of claim 15, further including a head cover above the turbine runner, wherein the actuators are mounted to the head cover above the circumference of the ring gate.

26. A method for controlling movement of a ring gate in a hydraulic turbine installation including a turbine runner rotating on a longitudinal axis, the ring gate being concentric with the runner and disposed for longitudinal movement between an open position in which water flow impinges on the runner and a closed position - 22 - in which the water flow is shut off, the movement of the ring gate controlled by a ring gate control system including an electrical control circuit, a set of actuators installed in longitudinal alignment with and distributed around a circumference of the ring gate, and a set of operating rods connecting the actuators to the circumference of the ring gate, the method comprising: setting a desired direction and approximate speed for the set of actuators; monitoring the set of actuators to detect -at least one actuator lagging or leading other actuators; and adjusting the speed of the at least one actuator to synchronize the set of actuators and thereby control the movement of the ring gate.

27. The method of claim 26, wherein the actuators are hydraulic cylinders and the ring gate control system further includes a set of metering devices fluidly coupled to associated cylinders of the set of cylinders and an electrically operated valve assembly including at least one electrical input, the valve assembly disposed to fluidly couple the set of metering devices to a fluid source or sump and to control a flow of hydraulic fluid therebetween in response to electric control signals applied to the at least one electrical input from the electrical control circuit, the setting of the desired direction and, speed step comprising: sending an electrical signal indicative of the desired direction and the approximate speed to the at least one electrical input of the valve assembly.

28. The method of claim 27, wherein the ring gate control system further includes a set of electrical valves fluidly coupled to associated cylinders of the set of cylinders, each electrical valve disposed to fluidly couple an associated cylinder to the fluid source or - 23 - sump, each electrical valve discharging hydraulic fluid from the associated cylinder into the source or sump in response to electric control signals applied to the at least one electrical input from the electrical control circuit, the adjusting of the speed step comprising: sending an electrical signal indicative of a desired speed adjustment to the at least one electrical input of the electrical valve associated with the leading or lagging cylinder.

29. The method of claim 28, wherein each hydraulic cylinder has a movable piston located in a chamber thereof which divides the chamber into a lower side and an upper side, and wherein each metering device of the set of metering devices and each electrical valve of the set of electrical valves is fluidly coupled to the lower side of the chamber of the associated cylinder, the adjusting of the speed step further comprising: discharging a flow of hydraulic fluid from the lower side of the chamber through the electrical valve associated with the leading or lagging cylinder.

30. The method of claim 27, wherein the hydraulic cylinders have movable pistons located in chambers of the cylinders, the ring gate control system further including an electrical controller and a set of sensors associated with the set of cylinders, the monitoring step comprising: selectively generating electrical signals with the sensors, the signals being indicative of positions of the pistons in the chambers; and receiving and processing the electrical signals with the electrical controller to detect at least one piston out of position with respect to other pistons.

31. A method for facilitating maintenance of turbine components in a hydraulic turbine installation - 24 - including a turbine runner rotating on a longitudinal axis, a head cover, a discharge ring, and a ring gate concentric with the runner and disposed for longitudinal movement between a raised position and lowered position, the ring gate having a lower circumference adjacent the head cover in the raised position and adjacent the discharge ring in the lowered position, the movement of the ring gate controlled by a ring gate control system including an electrical control circuit and a set of actuators distributed around an upper circumference of the ring gate and connected thereto, the method comprising : raising the ring gate to obtain a desired clearance distance between the ring gate and the discharge ring; positioning a plurality of jacking supports in the clearance distance beneath the ring gate; and lowering the ring gate until the head cover is lifted a desired distance above the runner.

32. The method of claims 31, wherein the positioning step comprises inserting the jacking supports beneath the ring gate in longitudinal alignment with a lower circumference of the ring gate.

33. The method of claims 32, wherein the inserting step comprises distributing the jacking supports at generally equidistant locations from each other around the lower circumference.

34. The method of claims 31, wherein the plurality of jacking supports comprises at least three jacking supports .